Re: Long life lights

JosephKK wrote:
On Thu, 4 Sep 2008 23:21:00 +0000 (UTC), don@xxxxxxxxxxxxxx (Don
Klipstein) wrote:

In article <NeydnUT0OMvNwSDVnZ2dnUVZ_sWdnZ2d@xxxxxxxxxxx>, Eric wrote:
Don Klipstein wrote:
In article <opdjb4tfqpjptb517apn9fv8i6hk12gfot@xxxxxxx>, JosephKK wrote:
On Sun, 24 Aug 2008 13:27:49 -0500, "Tim Williams"
<tmoranwms@xxxxxxxxxxx> wrote:

I've got a problem. I happen to carry the distinction of being the one responsible for changing lights. Much as that's a problem in itself, the biggest problem is.....the front porch light (surprisingly, it's not a stairway light, eh?), which happens to be a hanging, upside-down, enclosed fixture. And they put two screws in the thing, so it's almost impossible for a single person to replace the bulb thus inserted. Really quite remarkable how no one thought of this.

Besides modifying it, which I may consider because it's just that bad, in the mean time I need something that'll last. We've already tried the "ten gajillion hour" CFLs, which died in all of, you know it, three months. I'm guessing something high voltage (130V+?) and incandescent. Any recommendations?
They are still expensive as heck, but you can get LED lamps. Perhaps
below US$50 each for 100W equivalent, but always over 30,000 power on
hours life and some (more expensive) are rated at over 100,000 hours
power on.
Buyer beware for life expectancy of LED "lightbulbs" and the like, especially if they are white ones.

100,000 hours is a widely-repeated number, to the point of "conventional wisdom".

White LEDs often fade significantly well before then - I dare to say they mostly do. Colored LEDs, on the other hand, appear to me to have most operated for 100,000 hours or more to be keeping on trucking rather well after working for so long.

It appears to me that better heatsinkable white LEDs take 50,000 hours to fade by 30% at "characterizing current" ("typical current") when heatsunk to what I call a "moderately conservative extent". Much longer life expectancy as in 100,00-plus hours appears to me reasonable if they are both significantly underpowered and heatsunk to extent to keep the junction temperature well below the "old traditional" maximum recommended LED junction operating temperature of 85 C. In general, LEDs are more efficient when cooler and most blue, white, and non-yellowish-green ones
are more efficient when moderately or moderately severely underpowered - even regardless of temperature.

A main difference between white LEDs and most colored ones is that white LEDs normally have a phosphor and over 99.9% of colored ones I have seen don't.
The few colored LEDs that I have seen with phosphor are pastels, pink, lavendar/"purple" (as opposed to "violet", which is nearly-UV or an indigo-bluish-violet color with some "blacklight" effects), or a non-amberish maybe-slightly-chartreusish yellow close to 255-255-0 on a usual monitor.
Also beware - violet and UV LEDs with epoxy bodies tend to age fast due to UV or nearly-UV being hard on the epoxy.

I have seen sone reasonably credible numbers for even better 5 mm / T1-3/4 LEDs to fade significantly (don't know whether by 30% or 50%) in
as little as 6,000 to 10,000 hours. I don't know whether this is at
"characterizing current" of 20 mA or at maximum current of 30 mA. Some of this is news years old and some I got more recently.

One model of a white LED nightlight that I tried had "half-life" close to half a year. I would prefer green or blue LED nightlights over white
ones for better life expectancy as well as having a spectrum more favorable for stimulating "scotopic vision" ("night vision").

- Don Klipstein (don@xxxxxxxxx)
Instead of using white LEDs would it not be possible to use a number of
red, green, and blue LEDs create the effect of white light?
They actually do that. It gives a wierd color rendering effect - with red objects coming out "day-glo" bright and wood tones coming up very
reddish/pinkish. Oak has a color like that of mahogany. Skin tones come up reddish.

- Don Klipstein (don@xxxxxxxxx)

So how do they make the jumbotrons?
The DLP tv I have uses red, blue, and green LED's instead of a lamp and color wheel.. white screen is nice and white.. but I don't know how that
would translate to a lighting application..

Eric
.

Relevant Pages

  • Re: Long life lights
    ... Buyer beware for life expectancy of LED "lightbulbs" and the like, ... White LEDs often fade significantly well before then - I dare to say ... It appears to me that better heatsinkable white LEDs take 50,000 hours ... The few colored LEDs that I have seen with phosphor are pastels, pink, ...
    (sci.electronics.design)
  • Re: Long life lights
    ... White LEDs often fade significantly well before then - I dare to say ... It appears to me that better heatsinkable white LEDs take 50,000 hours ... The few colored LEDs that I have seen with phosphor are pastels, pink, ... Don Klipstein ...
    (sci.electronics.design)
  • Re: Long life lights
    ... Buyer beware for life expectancy of LED "lightbulbs" and the like, ... White LEDs often fade significantly well before then - I dare to say ... White LEDs are for most purposes are a variation of fluorescent lamps. ... And it still surprises people. ...
    (sci.electronics.design)
  • Re: how to connect up bulk leds ?
    ... ordered 100, 10 mm white leds. ... will be using around 70-90 leds. ... As LED's are driven with current rather than voltage, ... current-limiting resistor. ...
    (sci.electronics.design)
  • Re: Technics A1000 power amp - the lights have gone out !!!
    ... Blue LEDs, particularly, offer ... * Blue LEDs are far and away the best types to use for various reasons. ... * White LEDs are not much more efficient than a decent halogen lamp. ... than the longlife lamps typically used in audio equipment, ...
    (uk.rec.audio)